Watertight doors are a common safety feature of marine vessels. As in land based situations, doors may be pivoted on hinges, normally about a vertical axis, or they may be sliding. Sliding doors are particularly desired in marine vessels in cases where a lift opens onto a deck and it is desired not to obstruct a passageway that extends transversely of the lift immediately outside the lift exit. However, they are not limited to such situations and can be desirable wherever a passageway extends transversely to a compartment accessed by a doorway. However, pivoted doors remain also important where a passageway only extends longitudinally or where there is no disadvantage in the door panel swinging into a space accessed by the door, which is frequently the case.
Indeed, swinging doors are much less complex to install and do not need a wall space to one side of the door in which a sliding door is stowed when open. Such swinging doors in marine vessels normally comprise a peripheral lip of a frame for the door and against which the door seals when closed. Conveniently, the seal is in a single plane, normally, although not exclusively, in the vertical plane with elements serving to press the door against the frame seal. Hydrostatic pressure (in the case of flooding) on the door side of such a frame generally assists maintenance of the seal, but frequently the ability to seal in both directions is needed (ie, also if the flooding is on the bulkhead side of the door). In that event, lock members are needed to hold and press the door against the frame seal, and be sufficiently strong to resist water pressure that may be pressing against the frame side of the door attempting to open it. In either case, the seal needs to react against the pressure applied by the lock elements and potentially also against hydrostatic pressure of flood water. Conveniently, the seal is formed on a circumferential flange disposed around the door frame that serves to provide a rigid edge that is unlikely to deflect and open a leak path. Such a circumferential flange, however, needs to be raised above a floor level because, generally, a bottom edge of the door needs to press against the seal and is generally opened in a direction transverse to the seal, requiring the door itself to have some clearance above the floor. This means that a step is inevitably formed in the doorway opening above floor level. This makes access through the door problematic for wheeled vehicles. Since watertight doors may frequently be required in parts of vessels needing vehicular access, this represents an obstacle.
DK-1450/91, GB-A-1158472, GB-A-764782, JP-A-10-37626 and GB-A-2364731 all disclose door frame sills that have vertically displaceable seals that seal against the underside of a door and which are deflectable downwardly when, for example, a wheel overrides the seal. However, such arrangements are only effective for the purpose of excluding adverse weather, and are not watertight for the purpose of resisting flood.
WO-A-2009/008749 discloses a similar arrangement except that the seal element is selectively withdrawn and raised. The seal is arranged transverse to the door opening direction but is nevertheless only a weather seal and is not watertight, at least not against flood water.
Returning to sliding doors, the same problem exists. In order to provide a seal, this can only reliably be achieved by a circumferential seal between the door and frame and against which the door is pressed when closed. This pressing is in a direction transverse, indeed, most likely orthogonal, to the normal opening movement of the door. Thus the frame requires a circumferential lip against which the door can press and this results in the need for a step in the doorway. Furthermore, sliding doors present difficulties in resisting anticipated loads against the door when closed, particularly hydrostatic pressure of flood water on the frame side of the door. Rendering the door panel itself sufficiently rigid is not problematic, but holding it reliably in place is not straightforward.
Another issue with marine doors, both sliding and pivot-opening, is the need to resist fire. This also applies in both directions (at least, in some instances). Furthermore, not only is there the necessity to hold back a fire, but there is also the desire for a door to remain operational after a fire. Of course, there are limits to the operational functionality of any door system, but there are presently defined fire standards which door systems need, on occasions, to meet. Such standards may change, but a fire standard presently applicable for many marine vessels is A60 set under the International Convention for the Safety of Life at Sea (SOLAS), 1974 by the International Maritime Organisation (IMO). This standard requires a door to resist a fire on one side of the door that reaches temperatures of 1500° C., and for a period of at least one hour. The resistance to the fire is not just in respect of heat, but of course also in respect of gases, whether hot or toxic, within the fire environment that must remain confined thereto.
It is an object of the present invention to provide a door seal arrangement that is effective for a watertight door and convenient for vehicular access through the door. It is an object also to provide a fire resistant door that meets current standards.